Allow overriding the authnRequestBinding option per IdP in the MultiSamlStrategy

[bradydoll]

Currently the authnRequestBinding configuration applies to all Identity Providers when using the MultiSamlStrategy.

This moves the option from the Strategy object to the SAML object so the getSamlOptions function from the MultiSamlStrategy can override it per Identity Provider.

[brodly]

@bradydoll wondering if you could fix the conflicts here and push. just discovered this issue myself and looks like you have the same solution as me

[cjbarth]

This makes sense, however, there is a merge conflict. Can you resolve them?

[bradydoll]

I hope to have some time over the next week to fix the merge conflicts.

[bradydoll]

I finally got a chance to resolve these.

[cjbarth]

@bradydoll @bradydoll , could you please have a look at #529 and see if that addresses this PR. If so, can we close this in favor of that PR?